1. Field of the Invention
The present invention relates to an in-plane switching mode liquid crystal display (LCD) device capable of enhancing an aperture ratio and effectively preventing a light leakage phenomenon, and its fabrication method.
2. Description of the Related Art
A twisted nematic mode LCD device, which is commonly used for a high picture quality and low power consumption flat panel display device, has a disadvantage in that its viewing angle is too narrow. This results from a refractive anisotropy of liquid crystal molecules. That is, when a voltage is applied, liquid crystal molecules parallel to a substrate are rotated to be aligned in an almost vertical direction.
Thus, recently, an in-plane switching mode LCD has been actively studied in order to solve the narrow viewing angle problem by aligning the liquid crystal molecules in an almost horizontal direction.
FIGS. 1 and 2 illustrate a pixel unit of a general in-plane switching mode LCD, wherein FIG. 1 is a plan view and FIG. 2 is a sectional view taken along line I-I′.
As shown in FIGS. 1 and 2, a gate line 1 and a data line 3 are respectively arranged horizontally and vertically to define a pixel region on a transparent first substrate 10. In an LCD device, the N number of gate lines and the M number data lines cross each other to form the N×M number of pixels. In the drawing, only one pixel is shown for the sake of illustration.
In the pixel region, a thin film transistor (TFT) 9 including a gate electrode 1a, a semiconductor layer 5 and source/drain electrodes 2a and 2b is disposed at a crossing of the gate line 1 and the data line 3. The gate electrode 1a and the source/drain electrodes 2a and 2b are connected with the gate line 1 and the data line 3, respectively. In addition, a gate insulation film is stacked entirely over the substrate.
In the pixel region, a common line 4 is arranged to be parallel to the gate line 1, and a pair of electrodes, namely, a common electrode 6 and a pixel electrode 7, for switching the liquid crystal molecules are arranged in parallel. The common electrode 6 is connected with the common line 4 formed together with the gate electrode 1a, and the pixel electrode 7 is connected with the drain electrode 2b of the TFT 9 formed together with the source/drain electrodes 2a and 2b. 
A passivation film 11 and a first alignment film 12a are coated entirely over the substrate including the source/drain electrodes 2a and 2b. The common electrode 6 is formed at an outer edge of the pixel region in order to shield a horizontal electric field generated between the pixel electrode 7 formed at the outer edge of the pixel region and the data line 3. A pixel electrode line 14 overlaps with the common line 4 to form a storage capacitor (Cst) with an insulation film 8 interposed therebetween.
In order to prevent a light leakage between pixels, a black matrix 21 is formed at the gate line 1 and the data line 3. A color filter 23 corresponding to each pixel and an overcoat film 25 is formed on the black matrix 21, and a second alignment film 12b is coated on the overcoat film 25. A liquid crystal layer 13 is formed between the first and second substrates 10 and 20.
In the in-plane switching mode LCD with such a structure, when a voltage is not applied, liquid crystal molecules in the liquid crystal layer 13 are aligned along an alignment direction of the first and second alignment films 12a and 12b. When a voltage is applied between the common electrode 6 and the pixel electrode 7, the liquid crystal molecules are aligned in a direction vertical to an extending direction of the common electrode 6 and the data line 3. As mentioned above, since the liquid crystal molecules are switched on the same plane in the liquid crystal layer 13, gray levels are not inverted in viewing angle directions of the up/down direction and the left/right direction.
In the related art in-plane switching mode LCD device, constructed as described above, since the common electrode 6 and the pixel electrode 7 made of an opaque metal are formed in the pixel region, the aperture ratio is reduced.
In addition, in the related art in-plane switching mode LCD device, the first and second substrates must be constructed such that the black matrix 21 can be arranged at positions corresponding to the TFT 9, the gate line 1 and the data line 3 of the first substrate. However, when the two substrates are attached, they may be misaligned to generate light leakage. Thus, in consideration of the alignment margin, the area for forming the black matrix needs to be wider than the areas corresponding to the TFT 9, the gate line 1 and the data line 3. In this case, however, the increase in the area for formation of the black matrix aimed for preventing the light leakage due to the misalignment also reduces the aperture ratio.